Display device

ABSTRACT

A display device includes a transparent substrate, and a plurality of single-crystal thin-film semiconductor light-emitting elements disposed on one side of the transparent substrate. Each of the single-crystal thin-film semiconductor light-emitting elements is composed of single-crystal thin-film semiconductor layers separated from a base substrate, and includes a light-emitting layer and two non-light-emitting layers disposed on both sides of the light-emitting layer.

BACKGROUND OF THE INVENTION

The present invention relates to a display device using a single-crystalthin-film semiconductor light-emitting element.

A single-crystal semiconductor light-emitting element has a longerlifetime and can be driven with a larger current, compared with ageneral light-emitting element using organic material. Therefore, thesingle-crystal semiconductor light-emitting element is advantageous foraccomplishing a long-life and high-intensity light-emitting element. Thesingle-crystal thin-film semiconductor light-emitting element includes alight-emitting region formed on a base substrate. Generally, in adisplay device, the single-crystal semiconductor light-emitting elementis mounted on a transparent substrate in such a manner that thelight-emitting region faces the transparent substrate. Light emitted bythe light-emitting region toward the transparent substrate passes thetransparent substrate, and is emitted outside. In contrast, lightemitted by the light-emitting region in the opposite direction (i.e.,toward the base substrate) is absorbed by the base substrate, and is notemitted outside.

For example, Japanese Laid-Open Patent Publication No. H6-250591discloses a display device including an LED chip mounted on atransparent substrate. The LED chip includes a light-emitting regionformed on a semiconductor substrate (as a base substrate). Thelight-emitting region side of the LED chip is bonded onto thetransparent substrate using micro-bump bonding method or the like. Lightemitted by the light-emitting region toward the transparent substratepasses through the transparent substrate, and is emitted outside. Incontrast, light emitted by the light-emitting region in the oppositedirection (i.e., toward the base substrate) is absorbed by the basesubstrate, and is not emitted outside.

SUMMARY OF THE INVENTION

The present invention is intended to provide a display device includingat least one single-crystal thin-film semiconductor light-emittingelement disposed on one side of a transparent substrate, and capable ofemitting light form both sides.

According to an aspect of the present invention, there is provided adisplay device including a transparent substrate and a plurality ofsingle-crystal thin-film semiconductor light-emitting elements disposedon one side of the transparent substrate. Each of the single-crystalthin-film semiconductor light-emitting elements is composed ofsingle-crystal thin-film semiconductor layers separated from a basesubstrate, and includes a light-emitting layer (for example, an activelayer) and two non-light-emitting layers disposed on both sides of thelight-emitting layer.

With such a configuration, the base substrate (for forming thesingle-crystal thin-film semiconductor light-emitting element) does notexist in the display device, and therefore lights emitted by thelight-emitting layer are emitted outside.

Further scope of applicability of the present invention will becomeapparent from the detailed description given hereinafter. However, itshould be understood that the detailed description and specificembodiments, while indicating preferred embodiments of the invention,are given by way of illustration only, since various changes andmodifications within the spirit and scope of the invention will becomeapparent to those skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

In the attached drawings:

FIGS. 1A, 1B, 1C and 1D are perspective views for illustrating amanufacturing process of single-crystal thin-film semiconductorlight-emitting elements of a display device according to the firstembodiment of the present invention;

FIG. 2 is a sectional view showing a display device including thesingle-crystal thin-film semiconductor light-emitting element accordingto the first embodiment of the present invention;

FIGS. 3A and 3B are respectively a sectional view and a plan viewshowing the display device according to the first embodiment of thepresent invention;

FIG. 4 is a plan view showing a structure and operation of the displaydevice according to the first embodiment of the present invention;

FIG. 5A is a sectional view showing a display device according toExample 1-1 of the first embodiment of the present invention;

FIG. 5B is a sectional view showing a display device according toExample 1-2 of the first embodiment of the present invention;

FIG. 5C is a sectional view showing a display device according toExample 1-3 of the first embodiment of the present invention;

FIG. 6 is a plan view showing a display device according to Modification1-1 of the first embodiment of the present invention;

FIG. 7 is a plan view showing a single-crystal thin-film semiconductorlight-emitting element of three-terminal type according to Modification1-2 of the first embodiment of the present invention;

FIG. 8 is a sectional view showing a display device includingsingle-crystal thin-film semiconductor light-emitting elements accordingto the second embodiment of the present invention;

FIG. 9 is a plan view showing a structure and operation of the displaydevice according to Example 2-1 of the second embodiment of the presentinvention;

FIG. 10 is a sectional view showing the display device according toExample 2-1 of the second embodiment of the present invention;

FIG. 11 is a sectional view showing AlGaInP-based single-crystalthin-film semiconductor light-emitting elements according to Example 2-2of the second embodiment of the present invention;

FIG. 12 is a sectional view showing GaN-based single-crystal thin-filmsemiconductor light-emitting elements according to Example 2-3 of thesecond embodiment of the present invention;

FIG. 13 is a plan view showing single-crystal thin-film semiconductorlight-emitting elements according to Example 2-4 of the secondembodiment of the present invention;

FIG. 14 is a sectional view showing a display device includingsingle-crystal thin-film semiconductor light-emitting elements accordingto the third embodiment of the present invention;

FIG. 15 is a plan view showing a structure and operation of the displaydevice according to the third embodiment of the present invention;

FIG. 16 is a plan view showing a display device including single-crystalthin-film semiconductor light-emitting elements according to Example 3-1of the third embodiment of the present invention;

FIG. 17 is a plan view showing a display device including single-crystalthin-film semiconductor light-emitting elements according toModification 3-1 of the third embodiment of the present invention, and

FIG. 18 is a plan view showing a display device including single-crystalthin-film semiconductor light-emitting elements according to Example 3-2of the third embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Hereinafter, embodiments of the present invention will be described withreference to the attached drawings. In this regard, the drawings areschematically illustrated in order to facilitate understanding of theinvention. The present invention is not limited to specific preferableexamples (such as numerical values, conditions or the like) describedbelow, but can be modified without departing from the scope of theinvention. In the attached drawings, hatchings or the like are omittedas appropriate in order to avoid complexity.

First, a description will be made of a manufacturing process ofsingle-crystal thin-film semiconductor light-emitting elements ascomponents of a display device according to embodiments of the presentinvention.

<Manufacturing Process of Single-Crystal Thin-Film SemiconductorLight-Emitting Element>

FIGS. 1A though 1D show manufacturing process of single-crystalthin-film semiconductor light-emitting elements 111 according toembodiments of the present invention. In this manufacturing process,first, single-crystal thin-film semiconductor layers 102 are formed on abase substrate 101 via a sacrificial layer 103 using Metal OrganicChemical Vapor Deposition (MOCVD) method or the like according tospecifications of the single-crystal thin-film semiconductorlight-emitting elements 111. Then, the single-crystal thin-filmsemiconductor layers 102 are etched (patterned) into separate sectionsas shown in FIG. 1A according to the specifications of thesingle-crystal thin-film semiconductor light-emitting elements 111 so asto expose at least the sacrificial layer 103. This separation etchingcan be performed using wet etching method or dry etching method. In thisregard, the etching rate of the sacrificial layer 103 needs to be higherthan the etching rate of the single-crystal thin-film semiconductorlayers 102 and the etching rate of the base substrate 101.

Next, the sacrificial layer 103 is selectively etched (removed)utilizing a difference between the etching rate of the sacrificial layer103 and the etching rate of the base substrate 101 and thesingle-crystal thin-film semiconductor layers 102, so as to separate thesingle-crystal thin-film semiconductor layers 102 (as single-crystalthin-film semiconductor light-emitting elements 111) from the basesubstrate 101 as shown in FIG. 1B. Although not shown in FIGS. 1Athrough 1D, a supporting body is provided on the single-crystalthin-film semiconductor layers 102, and is used to support thesingle-crystal thin-film semiconductor layers 102 in the process ofseparating the single-crystal thin-film semiconductor layers 102 fromthe base substrate 101.

Then, the single-crystal thin-film semiconductor light-emitting elements111 (having been separated from the base substrate 101) are pressedagainst a transparent substrate 110 so that the single-crystal thin-filmsemiconductor light-emitting elements 111 adhere to the transparentsubstrate 110 as shown in FIGS. 1C and 1D. The single-crystal thin-filmsemiconductor light-emitting elements 111 are bonded onto thetransparent substrate 110 by means of intermolecular force. In thisregard, no adhesive agent is provided between the transparent substrate110 and the single-crystal thin-film semiconductor light-emittingelements 111. Thereafter, the supporting body (not shown) provided onthe single-crystal thin-film semiconductor light-emitting element 111 isremoved.

<Thickness of Single-Crystal Thin-Film Semiconductor Light-EmittingElement>

The thickness of the single-crystal thin-film semiconductorlight-emitting element 111 is preferably in a range from 0.3 μm to 10μm. The lower limit (0.3 μm) of the thickness is determined in order toobtain a light-emitting element with high output-efficiency using thesingle-crystal thin-film semiconductor layers 102. The upper limit (10μm) of the thickness is determined in order to form interconnectionwirings (for connecting electrodes on the single-crystal thin-filmsemiconductor light-emitting elements 111 and electrodes on thetransparent substrate 110) using photolithographic technology withoutcausing disconnection or defect, and is determined in consideration ofsafety coefficient.

<Transparent Substrate>

The transparent substrate 110 can be composed of, for example, glass,plastic, quarts, sapphire, oxide (such as ZnO) or nitride (such as GaN,AlN or SiN). The transparent substrate 110 has high opticaltransmittance of light emitted by single-crystal thin-film semiconductorlight-emitting element 111 formed on the transparent substrate 110.Although the optical transmittance is determined based on application,it is preferable that the optical transmittance of the transparentsubstrate 110 is higher than or equal to 50% to the light emitted by thesingle-crystal thin-film semiconductor light-emitting element 111.

<Bonding Structure>

As describe above, the single-crystal thin-film semiconductorlight-emitting elements 111 are preferably directly bonded onto thetransparent substrate 110 by means of intermolecular force without usingadhesive agent. However, it is also possible to provide a transparentdielectric layer on the transparent substrate 110, and to directly bondthe single-crystal thin-film semiconductor light-emitting elements 111onto the dielectric layer. Further, it is also possible to provide atransparent adhesive material layer on the transparent substrate 110,and to cause the single-crystal thin-film semiconductor light emittingelement 111 to adhere to the transparent adhesive material layer.

<Device Structure>

Next, descriptions will be made of a structure and light-emittingfunction of a display device including the single-crystal thin-filmsemiconductor light-emitting element 111 on the transparent substrate110 according to the first embodiment of the present invention.

FIG. 2 is a sectional view showing a display device 10 including thesingle-crystal thin-film semiconductor light-emitting element 111disposed on the transparent substrate 110 according to the firstembodiment of the present invention. As shown in FIG. 2, the displaydevice 10 of the first embodiment is configured so that thesingle-crystal thin-film semiconductor light-emitting element 111 isdirectly bonded onto the transparent substrate 110, and light is emittedfrom both sides of the single-crystal thin-film semiconductorlight-emitting element 111. The single-crystal thin-film semiconductorlight-emitting element 111 includes a light-emitting layer (i.e., anactive layer) 113 and two non-light-emitting layers 112 and 114 disposedon both sides of the light-emitting layer 113. Each of thenon-light-emitting layers 112 and 114 has a higher energy band gap thanthe light-emitting layer 113, so as to reduce absorption of light(emitted by the light-emitting layer 113) by the non-light-emittinglayers 112 and 114. With such a structure, lights 115 and 116 emitted bythe light-emitting layer 113 are emitted from both sides of thesingle-crystal thin-film semiconductor light-emitting element 111.Therefore, it becomes possible to accomplish the display device 10 thatindependently displays images on both sides of the transparent substrate110 using the lights 115 and 116 emitted by the single-crystal thin-filmsemiconductor light-emitting element 111 disposed on one side of thetransparent substrate 110. In this regard, it is more preferable thatthe thickness of the single-crystal thin-film semiconductorlight-emitting element 111 is in a range from 2 μm to 3 μm.

In the first embodiment, the single-crystal thin-film semiconductorlight-emitting element 111 has a double-heterojunction structure inwhich the light-emitting layer (i.e., the active layer) 113 issandwiched between the non-light-emitting layers 112 and 114 each ofwhich has a higher energy band gap than the light-emitting layer 113.However, the single-crystal thin-film semiconductor light-emittingelement 111 can have a single-heterojunction structure in which thenon-light-emitting layer having a higher energy band gap is disposed onone side of the light-emitting layer. Furthermore, the single-crystalthin-film semiconductor light-emitting element 111 can have ahomostructure in which the non-light-emitting layer is disposed on oneside of the light-emitting element, and the non-light-emitting layer hasthe same composition (i.e., the same energy band gap) as thelight-emitting layer but has different conductivity type. If thehomostructure is employed, it is also possible to providenon-light-emitting layers (as contact layers or intermolecular-forcebonding layers) having lower energy band gap than the active layer (thelight-emitting layer) on both sides of the active layer constituting ahomojunction structure.

<Structure, Operation and Effect of Display Device>

Next, a description will be made of a structure, operation and effect ofthe display device 10 according to the first embodiment including thesingle-crystal thin-film semiconductor light-emitting elements 111.

In the display device 10 according to the first embodiment, thesingle-crystal thin-film semiconductor light-emitting elements 111 arebonded onto one side of the transparent substrate 110 and are arrangedtwo-dimensionally on one side of the transparent substrate 110. Lightemission data signals are sent to the respective single-crystalthin-film semiconductor light-emitting elements 111 (i.e., pixels) whichare two-dimensionally arranged. A direction (i.e., a scanning direction)along which the light emission data signals are sent to thesingle-crystal thin-film semiconductor light-emitting elements 111 isreversed at constant time intervals, and therefore the display device 10is able to display images equally on both sides of the transparentsubstrate 110.

FIGS. 3A and 3B are a sectional view and a plan view schematicallyshowing a structure of the display device 10 according to the firstembodiment. As described above, the single-crystal thin-filmsemiconductor light-emitting elements 111 are arranged two-dimensionallyon the transparent substrate 110. The single-crystal thin-filmsemiconductor light-emitting elements 111 are connected to wirings 150formed on the transparent substrate 110 and extending in a verticaldirection (i.e., y-direction) and in a horizontal direction (i.e.,x-direction). The wirings 150 are connected to a drive control circuit160 provided on the transparent substrate 110. In this regard, the drivecontrol circuit 160 is not necessarily provided on the transparentsubstrate 110, but can be provided on the outside of the transparentsubstrate 110.

FIG. 4 is a plan view for illustrating the structure and operation ofthe display device 10 according to the first embodiment. Thesingle-crystal thin-film semiconductor light-emitting elements 111respectively have light-emitting regions 141 and electrode regions 142.The light-emitting regions 141 and electrode regions 142 arerespectively connected via interconnection wirings 144 and 143 toy-direction wirings 151 and x-direction wirings 152 formed on thetransparent substrate 110. In a particular example shown in FIG. 4, theinterconnection wirings 144 extending from the light-emitting regions141 also function as electrode contacts on the light-emitting regions141.

The display device 10 according to the first embodiment has a drivecontrol circuit 160. The drive control circuit 160 turns on connectionsbetween the single-crystal thin-film semiconductor light-emittingelements 111 (which are supposed to emit lights) and the x-directionwirings 152, and sends the light emission data signals to thesesingle-crystal thin-film semiconductor light emitting element 111 viathe y-direction wirings 151 while scanning in a direction A so as todisplay an image for a constant time interval. Then, the drive controlcircuit 160 causes addresses of the single-crystal thin-filmsemiconductor light-emitting elements 111 (which are supposed to emitlights) to be left-right reversed, turns on the connections between thesingle-crystal thin-film semiconductor light-emitting elements 111(which are supposed to emit lights) and the x-direction wirings 152, andsends the light emission data signals to the single-crystal thin-filmsemiconductor light emitting element 111 via the y-direction wirings 151while scanning in a direction B (opposite to the direction A) so as todisplay an image for a constant time interval.

In this regard, it is also possible to employ an arrangement enablingactive matrix driving. In particular, for example, capacitance elements,transistors, and wirings (for operating the capacitance elements andtransistors) can be provided for the respective single-crystal thin-filmsemiconductor light-emitting elements 111. Further, the drive controlcircuit 160 can drive the capacitance elements and the transistors ofthe single-crystal thin-film semiconductor light-emitting elements 111(which are supposed to emit lights) while selecting the x-directionwirings 152 and the y-direction wirings 151 to cause thesesingle-crystal thin-film semiconductor light-emitting elements 111 toemit lights at the same time.

With such a configuration, it becomes possible to accomplish the displaydevice 10 having the drive control circuit 160 capable of displaying thesame images (i.e., patterns of light emissions) alternately on bothsides of the transparent substrate 110 respectively for constant timeperiods, and switching the image-displaying sides at constant timeintervals.

More specifically, the display device 10 with the two-dimensionallyarranged single-crystal thin-film semiconductor light-emitting elements111 displays image as follows: First, the connections between thesingle-crystal thin-film semiconductor light-emitting elements 111(which are supposed to emit lights) and the x-direction wirings 152 areturned on, and the light emission data signals are sent to thesesingle-crystal thin-film semiconductor light-emitting elements 111 viathe y-direction wirings 151 while scanning in the direction A. Withthis, the display device 10 displays a predetermined image as seen froma surface-side of the transparent substrate 110 (i.e., a bonding sideonto which the single-crystal thin-film semiconductor light-emittingelements 111 are bonded). In this state, a left-right reversed image canbe observed from a backside of the transparent substrate 110 (i.e.,opposite to the above describe bonding side of the transparent substrate110). After the image is displayed on the surface-side, the addresses ofthe single-crystal thin-film semiconductor light-emitting elements 111which are supposed to emit lights are left-right reversed, theconnections between these single-crystal thin-film semiconductorlight-emitting elements 111 and the x-direction wirings 152 are turnedon, and the light emission data signals are sent to these single-crystalthin-film semiconductor light-emitting elements 111 via the y-directionwirings 151 while scanning in the direction B opposite to the directionA. By switching the image-displaying sides at constant time intervals,the same images can be displayed for respectively constant time periodsalternately on both sides of the display device 110.

In this regard, it is also possible to select the x-direction wirings152 and the y-direction wirings 154 so as to cause the two-dimensionallyarranged single-crystal thin-film semiconductor light-emitting elements111 (which are supposed to emit lights) to emit lights at the same time.Also in this case, the same images can be displayed on both sides of thetransparent substrate 110 for predetermine time periods.

As described above, the display device 10 of the first embodimentincludes single-crystal thin-film semiconductor light-emitting elements111 arranged two-dimensionally on the transparent substrate 110, and isconfigured to emit lights from both sides of the transparent substrate110. Further, the display device 10 includes the drive control circuit160 that reverses the image-displaying sides of the transparentsubstrate 110 at constant intervals. Therefore, it becomes possible toaccomplish the display device 10 capable of displaying the same imagesalternately on both sides of the transparent substrate 110.

In this first embodiment, the left-right reversed patterns of lightemissions of the single-crystal thin-film semiconductor light-emittingelements 111 are alternately displayed on both sides of the transparentsubstrate 110 for constant time periods. However, it is also possible todisplay different images (i.e., images which are not left-right reversedwith respect to each other) on both sides of the transparent substrate110 at constant periods. Further, the single-crystal thin-filmsemiconductor light-emitting elements 111 are not necessarily arrangedregularly, for example, in a matrix of with rows (n) and columns (m).

Examples and Modifications of First Embodiment

Next, examples and modifications of the first embodiment will bedescribed with reference to FIGS. 5A to 8.

FIGS. 5A through 5C are sectional views showing structures ofsingle-crystal thin-film semiconductor light-emitting elements 111formed of typical compound semiconductor materials according to examplesof the first embodiment. In this regard, FIGS. 5A through 5Cschematically show structures of the single-crystal thin-filmsemiconductor light-emitting elements 11, and are not intended to showlayer-thicknesses and sizes of the single-crystal thin-filmsemiconductor light-emitting elements 111. The display devices of theexamples of the first-embodiment are not limited to those shown in FIGS.5A through 5C, but various modifications can be made.

Example 1-1

FIG. 5A is a sectional view showing a display device 10-1 of Example 1-1of the first embodiment including an AlGaAs-based single-crystalthin-film semiconductor light-emitting element 111-1 as a light source.

The single-crystal thin-film semiconductor light-emitting element 111-1includes the AlGaAs-based single-crystal thin-film semiconductorlight-emitting element 111-1 bonded onto the transparent substrate 110.The AlGaAs-based single-crystal thin-film semiconductor light-emittingelement 111-1 includes a GaAs layer 161, an Al_(t)Ga_(1−t)As layer 162,a GaAs layer 163, an Al_(x)Ga_(1−x)As 164, an Al_(y)Ga_(1−y)As layer(i.e., an active layer) 165, an Al_(z)Ga_(1−z)As layer 166 and a GaAslayer 167 laminated on the transparent substrate 110 in this order fromthe bottom (i.e., from the transparent substrate 110 side). The lights115 and 116 emitted by the Al_(y)Ga_(1−y)As layer (i.e., the activelayer) 165 are emitted outside from both sides of the transparentsubstrate 110. It is preferable that the compositional parameters (x, y,z and t) of the respective layers (i.e., Al content) satisfy therelationship: y<x, z, t.

Example 1-2

FIG. 5B is a sectional view showing a display device of Example 1-2 ofthe first embodiment including an AlGaInP-based single-crystal thin-filmsemiconductor light-emitting element 111-2 as a light source.

The single-crystal thin-film semiconductor light-emitting element 111-2includes a GaAs layer 171, an (Al_(t)Ga_(1−t))_(s1)In_(1−s1)P layer 172,a GaAs layer 173, an (Al_(x)Ga_(1−x))_(s2)In_(1−s2)P layer 174, an(Al_(y)Ga_(1−y))_(s2)In_(1−s2)P layer (i.e., an active layer) 175, an(Al_(z)Ga_(1−z))_(s2)In_(1−s2)P layer 176 and a GaAs layer 177 laminatedon the transparent substrate 110 (FIG. 5A) in this order from the bottom(i.e., from the transparent substrate 110 side). The compositionalparameters (x, y, z, s1 and s2) of the respective semiconductor layerspreferably satisfy the relationships 0.49≦s1=s2≦0.51, and y<x, z. Theactive layer 175 can have a laminated structure of(Al_(q)Ga_(1−q))_(s2)In_(1−s2)P/(Al_(r)Ga_(1−r))_(s2)In_(1−s2)P (i.e.,in which (Al_(r)Ga_(1−r))_(s2)In_(1−s2)P is laminated on(Al_(q)Ga_(1−q))_(s2)In_(1−s2)P). The thickness of the active layer 175can be set so as to obtain a quantum-well structure. The compositionalparameters (q, r and s2) of the active layer 175 can be determinedaccording to wavelength, for example, q=1, r=0 and s2=0.5.

Example 1-3

FIG. 5C is a sectional view showing a display device of Example 1-3 ofthe first embodiment including a GaN-based single-crystal thin-filmsemiconductor light-emitting element 111-3 as a light source.

The single-crystal thin-film semiconductor light-emitting element 111-3includes an AlN layer 181, a GaN layer 182, an active layer 183 with alaminated structure of In_(x)Ga_(1−x)N/GaN (i.e., in which a GaN layeris laminated on an In_(x)Ga_(1−x)N/GaN layer), an Al_(y)Ga_(1−y)N layer184 and a GaN layer 185 laminated on the transparent substrate 110 (FIG.5A) in this order from the bottom (i.e., the transparent substrate 110side). In this case, the GaN layer 182, the active layer 183 (i.e., theIn_(x)Ga_(1−x)N layer and the GaN layer) and the Al_(y)Ga_(1−y)N layer184 can be replaced with layers including an In_(x)Ga_(1−x)N layer (x≧0)as an active layer sandwiched between an n-Al_(z)Ga_(1−z)N layer (z≧0)and a p-Al_(y)Ga_(1−y)N layer (y≧0).

Modification 1-1

In the first embodiment and examples thereof, the single-crystalthin-film semiconductor light-emitting elements of the display device 10are not necessarily composed of the same material. For example, as shownin FIG. 6, the display device can include the single-crystal thin-filmsemiconductor light-emitting elements 111 a 111 b, 111 c which arecomposed of materials different from each other. In Modification 1-1,the display device 10-2 includes the single-crystal thin-filmsemiconductor light-emitting elements 111 a, 111 b and 111 crespectively configured as red, green and blue single-crystal thin-filmsemiconductor light-emitting elements that emit red, green and bluelights. With such a configuration, the display device 10-2 capable ofdisplaying color image can be accomplished. In such a case, the displaydevice 10-2 includes the single-crystal thin-film semiconductorlight-emitting elements 111 a, 111 b and 111 c, the transparentsubstrate 110, the y-direction wirings 153, the x-direction wirings 154and the drive control circuit 170 as described above.

Modification 1-2

In the examples and modification of the first embodiment, thetwo-terminal type light-emitting elements have been described. However,the single-crystal thin-film semiconductor light-emitting element of thefirst embodiment can be, for example, of three-terminal type as shown inFIG. 7. The three-terminal type single-crystal thin-film semiconductorlight-emitting element 111-4 of Modification 1-2 is an AlGaAs-basedsingle-crystal thin-film semiconductor light-emitting element. Morespecifically, the single-crystal thin-film semiconductor light-emittingelement 111-4 includes an n-GaAs layer 191, an n-Al_(t)Ga_(1−t)As layer192, an n-GaAs layer (i.e., a cathode contact layer) 193, ann-Al_(x)Ga_(1−x)As layer 194, an n-Al_(y)Ga_(1−y)As layer (i.e., anactive layer) 195, a p-Al_(z)Ga_(1−z)As layer 196, an n-Al_(r)Ga_(1−r)Aslayer (i.e., a gate contact layer) 197, a p-Al_(s)Ga_(1−s)Al layer 198,a p-GaAs layer (i.e., an anode contact layer) 199, an anode electrode201, a gate electrode 202 and a cathode electrode 203 laminated on thetransparent substrate 110 (FIG. 5A) in this order from the bottom (i.e.,from the not shown transparent substrate 110 side).

Second Embodiment

FIG. 8 is a sectional view showing a display device 20 according to thesecond embodiment of the present invention. As shown in FIG. 8, thedisplay device 20 includes another single-crystal thin-filmsemiconductor light-emitting element 121 laminated on the single-crystalthin-film semiconductor light-emitting element 111 (having beendescribed in the first embodiment) via a non-light-transmitting layer120. The upper single-crystal thin-film semiconductor light-emittingelement 121 includes a light-emitting layer (an active layer) 123 andnon-light-emitting layers 122 and 124 disposed on both sides of thelight-emitting layer 123. It is necessary that each of thenon-light-emitting layers 122 and 124 has a higher energy band gap thanthe light-emitting layer 123, as in the first embodiment. In the secondembodiment, a total thickness of the single-crystal thin-filmsemiconductor light-emitting elements 111 and 121 and thenon-light-transmitting layer 120 is preferably in a range from 4 μm to 7μm. Further, in the second embodiment, the non-light-transmitting layer120 reflects or absorbs the lights emitted by the light-emitting layers(i.e., the active layers) 113 and 123 toward the non-light-transmittinglayer 120. With such a structure, the lights 116, 117, 126 and 127emitted by the light-emitting layers (i.e., the active layers) 113 and123 can be emitted outside from both sides of the non-light-transmittinglayer 120 (i.e., the respective single-crystal thin-film semiconductorlight-emitting elements 111 and 121 sides). Therefore, the displaydevice 20 is able to independently display images on both sides of thetransparent substrate 110.

Furthermore, the display device 20 includes a drive control circuit 180(see FIG. 9) that independently controls light emissions of thesingle-crystal thin-film semiconductor light-emitting elements 111 and121 on both side of the non-light-transmitting layer 120.

Examples of Second Embodiment

Next, examples of the second embodiment will be described with referenceto FIGS. 9 to 13.

Example 2-1

A display device 20-1 of Example 2-1 includes AlGaAs-basedsingle-crystal thin-film semiconductor light-emitting elements. FIG. 9is a plan view showing the display device 20-1 according to Example 2-1of the second embodiment, including a plurality of AlGaAs-basedsingle-crystal thin-film semiconductor light-emitting elements. FIG. 10is a sectional view taken along line X-X in FIG. 9.

As shown in FIG. 9, the display device 20-1 includes a plurality oflaminated pairs of AlGaAs-based single-crystal thin-film semiconductorlight-emitting elements 220 and 230 (see FIG. 10) arrangedtwo-dimensionally on the transparent substrate 110. The AlGaAs-basedsingle-crystal thin-film semiconductor light-emitting elements 220 and230 have common electrodes 252 connected to common wirings 257, uppern-side electrodes 253 and lower n-side electrodes 254 respectivelyconnected to upper n-side control wirings 256 and lower n-side controlwirings 255. The drive control circuit 180 independently controls theupper and lower single-crystal thin-film semiconductor light-emittingelements 220 and 230.

As shown in FIG. 10, the lower single-crystal thin-film semiconductorlight-emitting element 230 includes an n-side conductive layer 234(n-GaAs/n-Al_(t)Ga_(1−t)As/n-GaAs), an n-Al_(z2)Ga_(1−z2)As layer 233,an n-Al_(y2)Ga_(1−y2)As layer (i.e., an active layer) 232 and ap-Al_(z2)Ga_(1−x2)As layer 231 laminated on the transparent substrate110 in this order from the bottom (i.e., from the transparent substrate110 side). A p-GaAs layer (i.e., a light absorbing layer) 240 as anon-light-transmission layer is formed on the single-crystal thin-filmsemiconductor light-emitting element 230. The upper single-crystalthin-film semiconductor light-emitting element 220 is formed on thep-GaAs layer 240. The upper single-crystal thin-film semiconductorlight-emitting element 220 includes a p-Al_(z1)Ga_(1−z1)As layer 224, ann-Al_(y1)Ga_(1−y1)As layer (i.e., an active layer) 223, ann-Al_(x1)Ga_(1−x1)As layer 222 and n-GaAs layer 221 laminated in thisorder from the p-GaAs layer 240 side. The common electrodes 252, theupper n-side electrodes 253, the lower n-side electrodes 254 and thelower n-side control wirings 255 or the like are provided on thesingle-crystal thin-film semiconductor light emitting elements 220 and230 via an insulation film 251 (as an interlayer insulation film).

In this Example 2-1, compositional parameters (x1, x2, y1, y2, z1 andz2) of Al satisfy the relationships: y1<x1, z1 and y2<x2, z2. When y1=y2is satisfied, the n-Al_(y1)Ga_(1−y1)As layer (i.e., the upper activelayer) 223 and the n-Al_(y2)Ga_(1−y2)As layer (i.e., the lower activelayer) 232 on both sides of the p-GaAs layer 240 (i.e., the lightabsorbing layer) emit lights having the same wavelengths. The thicknessof the p-GaAs layer (the light absorbing layer) 240 is, for example, ina range from 0.5 μm to 1 μm. With such a thickness, the p-GaAs layer 240absorbs the lights from the upper and lower active layers 223 and 232,and functions as non-light-transmitting layer. It is also possible toreplace the p-GaAs layer 240 with a layer of different conductivitytype, for example, a laminated structure including for example, ann-GaAs layer (on the p-Al_(z1)Ga_(1−z1)As layer 224 side), a highresistance GaAs layer and a p-GaAs layer (on the p-Al_(x2)Ga_(1−x2)Aslayer 231 side). In such a case, the upper single-crystal thin-filmsemiconductor light-emitting element 220 can be configured to include ann-AlGaAs layer 224, a p-AlGaAs layer 223, a p-AlGaAs layer 222 and ap-GaAs layer 221. The upper single-crystal thin-film semiconductorlight-emitting element 220 can have n-side and p-side electrodes whichare independent from those of the lower single-crystal thin-filmsemiconductor light-emitting elements 230, and other modifications canbe made.

The lights emitted by the light-emitting layers 223 and 232 of therespective single-crystal thin-film semiconductor light-emittingelements 220 and 230 and proceeding toward the p-GaAs layer 240 areabsorbed by the p-GaAs layer 240 (the light absorbing layer) as thenon-light-transmitting layer, and the lights proceeding in directionsaway from the p-GaAs layer 240 are emitted outside as emitted light 116and 126.

Example 2-2

A display device of Example 2-2 of the second embodiment includesAlGaInP-based single-crystal thin-film semiconductor light-emittingelements. FIG. 11 is a sectional view showing AlGaInP-basedsingle-crystal thin-film semiconductor light-emitting elements 320 and330 of the display device according to Example 2-2 of the secondembodiment.

The upper single-crystal thin-film semiconductor light-emitting element320 is formed on a p-GaAs layer (i.e., a light absorbing layer) 240 as anon-light-transmitting layer. The upper single-crystal thin-filmsemiconductor light-emitting element 320 includes ap-(Al_(x1)Ga_(1−x1))_(y1)In_(1−y1)P layer 321, ann-(Al_(x2)Ga_(1−x2))_(y1)In_(1−y1)P layer (i.e., an active layer) 322,an n-(Al_(x3)Ga_(1−x3))_(y1)In_(1−y1)P layer 323 and an n-GaAs layer 324laminated in this order from the bottom (i.e., from the p-GaAs layer 240side). In this regard, compositional parameters (x1, x2, x3 and y1) ofthe respective layers satisfy the relationships: 0.49≦y1≦0.51, x2<x1,x3. The lower single-crystal thin-film semiconductor light-emittingelement 330 below the p-GaAs layer 240 includes ap-(Al_(z3)Ga_(1−z3))_(y1)In_(1−y1)P layer 336, ann-(Al_(z2)Ga_(1−z2))_(y1)In_(1−y1)P layer (i.e., an active layer) 335,an n-(Al_(z1)Ga_(1−z1))_(y1)In_(1−y1)P layer 334, an n-GaAs layer 333,an n-(Al_(s1)Ga_(1−s1))_(y1)In_(1−y1)P layer 332 and an n-GaAs layer 331in this order from the top (i.e., from the p-GaAs layer 240 side). Inthis case, compositional parameters (y1, z1, z2, z3) of the respectivelayers satisfy the relationships: 0.49≦y1≦0.51, z2<z1, z3. Further, then-(Al_(z2)Ga_(1−z2))_(y1)In_(1−y1)P layer 335 (i.e., the active layer)can be replaced with a laminated structure such as(Al_(t1)Ga_(1−t1))_(y1)In_(1−y1)P/(Al_(t2)Ga_(1−t2))_(y1)In_(1−y1)P andhaving, for example, a non-dope type quantum-well structure.

Example 2-3

A display device of Example 2-3 of the second embodiment includesGaN-based single-crystal thin-film semiconductor light-emittingelements. FIG. 12 is a sectional view showing GaN-based single-crystalthin-film semiconductor light-emitting elements 340 and 350 of thedisplay device according to Example 2-3 of the second embodiment.

The upper single-crystal thin-film semiconductor light-emitting element340 is formed on an In_(x3)Ga_(1−x3)N layer (i.e., a light absorbinglayer) 360 as a non-light-transmitting layer. The upper single-crystalthin-film semiconductor light-emitting element 340 includes a p-GaNlayer 341, an active layer 342 (including a non-dope In_(x1)Ga_(1−x1)Nlayer 342 a and a non-dope GaN layer 342 b formed thereon), ann-Al_(y1)Ga_(1−y1)N layer 343 and an n-GaN layer 344 laminated in thisorder from the bottom (i.e., from the In_(x3)Ga_(1−x3)N layer 360 side).The lower single-crystal thin-film semiconductor light-emitting element350 below the In_(x3)Ga_(1−x3)N layer (i.e., the light absorbing layer)360 includes a p-Al_(y2)Ga_(1−y2)N layer 354, an active layer 353(including a non-dope In_(x2)Ga_(1−x2)N layer and a non-dope GaN layerformed thereon), an n-GaN layer 352 and an AlN layer 351 laminated inthis order from the top (i.e., from the In_(x3)Ga_(1−x3)N layer 360side). Compositions (x1, x2 and x3) of the layers preferably satisfy arelationship, for example, x3>x1, x2.

In this regard, the light absorbing layers (i.e., thenon-light-transmitting layers) of Examples 2-2 and 2-3 can be replacedwith reflection layers having laminated structures of AlGaAs-based orAlGaInP-based semiconductor layers such as AlAs/Al_(x)Ga_(1−x)As (x≧0)or GaN-based semiconductor layers such as AlN/Al_(x)Ga_(1−x)N (x≧0).

Example 2-4

A display device 20-2 of Example 2-4 of the second embodiment includesAlGaAs-based single-crystal thin-film semiconductor light-emittingelements, and a metal layer (i.e., a reflection layer) as anon-light-emitting layer provided therebetween. FIG. 13 is a sectionalview showing the display device 20-2 according to Example 2-4 of thesecond embodiment.

The display device 20-2 includes AlGaAs-based single-crystal thin-filmsemiconductor light-emitting elements 420 and 430 disposed on upper andlower sides of a metal layer 454 (i.e., a reflection layer or a commonelectrode) as a non-light-transmitting layer. The upper single-crystalthin-film semiconductor light-emitting element 420 includes a p-GaAslayer 425, a p-Al_(z1)Ga_(1−z1)As layer 424, an n-Al_(y1)Ga_(1−y1)Aslayer (an active layer) 423, an n-Al_(x1)Ga_(1−x1)As layer 422 and ann-GaAs layer 421 laminated in this order from the bottom (i.e., from themetal layer 454 side). The lower single-crystal thin-film semiconductorlight-emitting element 430 below the metal layer 454 (i.e., thereflection layer or the common electrode) includes a p-GaAs layer 431, ap-Al_(x2)Ga_(1−x2)As layer 432, an n-Al_(y2)Ga_(1−y2)As layer (i.e., anactive layer) 433, an n-Al_(z2)Ga_(1−z2)As layer 434 and an n-typeconductive layer 435 (n-GaAs/n-Al_(t)Ga_(1−t)As/n-GaAs) laminated inthis order from the top (i.e., from the metal layer 454 side).

In this example, the metal layer 454 (i.e., the reflection layer or thecommon electrode) also functions as a common electrode (i.e., the commonelectrode 252 described in Example 2-1). Therefore, the metal layer 454needs to be formed of metal which allows low-resistance ohmic-contactwith single-crystal thin-film semiconductor materials of the upper andlower single-crystal thin-film semiconductor light-emitting elements 420and 430. For example, if the single-crystal thin-film semiconductorlight-emitting elements are formed of AlGaAs-based or AlGaInP-basedsemiconductor materials, the metal layer 454 is formed of a laminatedstructure of Ti/Pt/Au/Ti or the like that allows low-resistanceohmic-contact with the GaAs layer. If the single-crystal thin-filmsemiconductor light-emitting elements are formed of GaN-basedsemiconductor materials, the metal layer 454 is formed of a laminatedstructure of, for example, Ni/Au/Ti or the like. The topmost Ti layer ofthe metal layer 454 is provided for enhancing adhesion to a dielectriclayer 461. The dielectric layer 461 is provided on the metal layer 454for bonding the metal layer 454 and the single-crystal thin-filmsemiconductor light-emitting element 420 to each other. In this example,the upper single-crystal thin-film semiconductor light-emitting element420 is directly bonded onto the dielectric layer 461 by means ofintermolecular force. Although it is preferable that the uppersingle-crystal thin-film semiconductor light-emitting element 420 isdirectly bonded onto the dielectric layer 461, the upper single-crystalthin-film semiconductor light-emitting element 420 can also be bondedonto the dielectric layer 461 using low-melting-point soldering,transparent conductive paste or adhesive agent or the like.

The metal layer 454 (as the common electrode), an upper n-side electrode452, a p-side electrode 453 and a lower n-side electrode 455 areprovided via an insulation film 451 as an interlayer insulation film.

In this example, the lights emitted by the light-emitting layers (theactive layers) 423 and 433 of the respective single-crystal thin-filmsemiconductor light-emitting elements 420 and 430 are reflected by themetal layer 454 (i.e., the reflection layer and the common electrode),and emitted outside from both sides of the transparent substrate 110 asemitted lights 116, 117, 126 and 127.

In the above description, the reflection layer (as thenon-light-transmitting layer) has been described as the metal layer.However, the reflection layer can be composed of a laminated structureof dielectric thin-films having largely different refractive indexes.For example, it is possible to use a laminated structure such asZrO₂/SiO₂, MgO/SiO₂ or the like, or a laminated structure includinglayers of material with high refractive index and material with lowrefractive index. The material with high refractive index is, forexample, HfO₂, Sc₂O₃, Y₂O₃, ThO, MgO, Al₂O₃ or the like. The materialwith low refractive index is, for example, NdF₃, LaF₃, ThF₄, SiO₂, MgF₂,LiF, NaF or the like. The reflection layer having the laminatedstructure can be provided between the dielectric layer 461 and the metallayer 454, and also can be used instead of the dielectric layer 461.

Third Embodiment

FIG. 14 is a sectional view showing a display device 30 according to thethird embodiment of the present invention. As shown in FIG. 14, in thedisplay device 30, first and second single-crystal thin-filmsemiconductor light-emitting elements 111 and 131 are disposed on oneside of the transparent substrate 110 so as to be adjacent to eachother. Further, a first non-light-transmitting layer 130 is disposed ona top of the first single-crystal thin-film semiconductor light-emittingelement 111. A second non-light-transmitting layer 140 is disposedbetween the second single-crystal thin-film semiconductor light-emittingelement 131 and the transparent substrate 110. The first single-crystalthin-film semiconductor light-emitting element 111 has the samestructure as the single-crystal thin-film semiconductor light-emittingelement 111 (FIG. 2) of the first embodiment. The second single-crystalthin-film semiconductor light-emitting element 131 includes alight-emitting layer (an active layer) 133 and non-light-emitting layers132 and 134 disposed on both sides of the light-emitting layer 133. Eachof the non-light-emitting layers 132 and 134 has a higher energy bandgap than the light-emitting layer 133. Each of the single-crystalthin-film semiconductor light-emitting elements 111 and 131 preferablyhas a thickness in a range from 2 μm to 3 μm. The non-light-transmittinglayers 130 and 140 reflect or absorb the lights emitted by thelight-emitting layers (i.e., the active layer) 113 and 133. Therefore,the lights 116 and 117 from the light-emitting layer 113 are emittedoutside from a side opposite to the first non-light-transmitting layer130 side, and the lights 136 and 137 from the light-emitting layer 133are emitted outside from a side opposite to the secondnon-light-transmitting layer 140.

A plurality of pairs of the single-crystal thin-film semiconductorlight-emitting elements 111 and 131 are arranged one-dimensionally ortwo-dimensionally. Further, the display device 30 has a drive controlcircuit 190 (see FIG. 15) that independently controls light emissions ofthe single-crystal thin-film semiconductor light-emitting elements 111and 131 on the transparent substrate 110.

With such a configuration, the display device 30 is able toindependently display images on both sides of the transparent substrate110. Further, sizes and arrangements of pixels can be different betweenboth sides of the transparent substrate 110.

Examples of Third Embodiment

Next, structures and operations of examples and modifications of thethird embodiment will be described with reference to FIGS. 15 through18.

Example 3-1

A display device 30-1 of Example 3-1 of the third embodiment includesAlGaAs-based single-crystal thin-film semiconductor light-emittingelements 520 and 530 as light sources. FIG. 15 is a sectional viewshowing the display device 30-1 according to Example 3-1 of the thirdembodiment, including the AlGaAs-based single-crystal thin-filmsemiconductor light-emitting elements 520 and 530. FIG. 16 is asectional view taken along Line XVI-XVI in FIG. 15.

In the display device 30-1, a plurality of pairs of the AlGaAs-basedsingle-crystal thin-film semiconductor light-emitting elements 520 and530 are arranged two-dimensionally on the transparent substrate 110. TheAlGaAs-based single-crystal thin-film semiconductor light-emittingelements 520 and 530 (on the left and right in FIG. 15) have commonelectrodes 554 connected to common wirings 573, and have metal wirings(the reflection layers) 553 and electrodes 552 respectively connected tocontrol wirings 571 and 572. The drive control circuit 190 independentlycontrols the single-crystal thin-film semiconductor light-emittingelements 520 and 530 (on the left and right in FIG. 15).

As shown in FIG. 16, the single-crystal thin-film semiconductorlight-emitting element 530 (on the right in FIG. 16) is formed on thetransparent substrate 110 and below the metal layer 553 (the reflectionlayer) as the first non-light-transmitting layer. The single-crystalthin-film semiconductor light-emitting element 530 includes a GaAs layer531, an Al_(z1)Ga_(1−z1)As layer 532, an Al_(y1)Ga_(1−y1)As layer (i.e.,an active layer) 533, an Al_(x1)Ga_(1−x1)As layer 534, a GaAs layer 535,an Al_(t1)Ga_(1−t1)As layer 536 and a GaAs layer 537 laminated in thisorder from the top (i.e., the metal layer 553 side). The single-crystalthin-film semiconductor light-emitting element 520 (on the left in FIG.16) is formed on the metal layer (the reflection layer) 560 as thesecond non-light-transmitting layer on the transparent substrate 110.The single-crystal thin-film semiconductor light-emitting element 520includes a GaAs layer 527, an Al_(t2)Ga_(1−t2)As layer 526, a GaAs layer525, an Al_(x2)Ga_(1−x2)As layer 524, an Al_(y2)Ga_(1−y2)As layer 523(i.e., an active layer), an Al_(z2)Ga_(1−z2)As layer 522 and a GaAslayer 521 laminated in this order from the bottom (i.e., from the metallayer 560 side). The common electrode 554, the metal layer 553 and theelectrode 552 are provided via an insulation film 551 as an interlayerinsulation film. The metal layer 553 also functions as an individualelectrode of the single-crystal thin-film semiconductor light-emittingelement 530 (on the right in FIG. 16). The electrode 552 functions anindividual electrode of the single-crystal thin-film semiconductorlight-emitting element 520 (on the left in FIG. 16). The metal layer(i.e., the reflection layer) 560 is formed of, for example, Ti,Ti/AuGeNi, Ti/Pt/Au, Ti/Cu, Ti/Pt or the like, and the metal layer(i.e., the reflection layer) 553 is formed of, for example, Ti,AuGeNi/Ti, Au/Pt/Ti, Cu/Ti, Pt/Ti or the like (in this regard, “A/B”means that “A is laminated on B”).

According to Example 3-1, the lights emitted by the light-emittinglayers 523 and 533 of the adjacent two single-crystal thin-filmsemiconductor light-emitting elements 520 and 530 are respectivelyreflected by the metal layers (the reflection layers) 553 and 560 asnon-light-transmitting layers, and emitted outside as emitted lights116, 117, 136 and 137.

Modification 3-1

In a modification of Example 3-1 (referred to as Modification 3-1), adisplay device 30-2 includes a dielectric layer 561 provided between thetransparent substrate 110 and the single-crystal thin-film semiconductorlight-emitting elements 520 and 530, as shown in FIG. 17. Structures ofthe single-crystal thin-film semiconductor light-emitting elements 520and 530, electrodes or the like of Modification 3-1 are the same asthose of Example 3-1. The display device 30-2 of Modification 3-1 isdifferent from the display device 30-1 of Example 3-1 in that thedisplay device 30-2 includes the dielectric layer 561. The dielectriclayer 561 can be formed of, for example, organic material layerinorganic or material layer (oxide layer or nitride layer) thattransmits the lights emitted by the light-emitting layers of thesingle-crystal thin-film semiconductor light-emitting elements 520 and530.

According to Modification 3-1, the lights emitted by the light-emittinglayers of the adjacent two single-crystal thin-film semiconductorlight-emitting elements 520 and 530 are respectively reflected by themetal layers (i.e., the reflection layers) 553 and 560 asnon-light-transmitting layers, pass through the dielectric layer 561,and are emitted outside as emitted lights 116, 117, 136 and 137.

Example 3-2

FIG. 18 is a sectional view showing a structure of a display device 30-3of Example 3-2 of the third embodiment. The structure and operation ofthe display device 30-3 will be described with reference to FIG. 18.

In the display device 30-3, AlGaAs-based single-crystal thin-filmsemiconductor light-emitting elements 620 and 630 respectively havelight absorbing layers 625 and 631 (as first and secondnon-light-transmitting layers) that absorb lights emitted by thelight-emitting layers of the single-crystal thin-film semiconductorlight-emitting elements 620 and 630. A plurality of pairs of theAlGaAs-based single-crystal thin-film semiconductor light-emittingelements 620 and 630 (on the left and right in FIG. 18) are arrangedtwo-dimensionally on the dielectric layer 561 on the transparentsubstrate 110. The respective AlGaAs-based single-crystal thin-filmsemiconductor light-emitting elements 620 and 630 are connected tocommon electrodes 554 and respectively have individual electrodes (i.e.,the metal layer 553 and the electrode 552) as described in Example 3-1.

More specifically, in the display device 30-3, the single-crystalthin-film semiconductor light-emitting element 630 on the right in FIG.18 is formed on the dielectric layer 561 and below the metal layer 553.The single-crystal thin-film semiconductor light-emitting element 630includes a GaAs layer (i.e., the light absorbing layer) 631, anAl_(z1)Ga_(1−z1)As layer 632, an Al_(y1)Ga_(1−y1)As layer (an activelayer) 633, an Al_(x1)Ga_(1−x1)As layer 634, a GaAs layer 635, anAl_(t1)Ga_(1−t1)As layer 636 and a GaAs layer 637 laminated in thisorder from the top (i.e., the metal layer 553 side). The single-crystalthin-film semiconductor light-emitting element 620 on the left in FIG.18 is formed on the dielectric layer 561 on the transparent substrate110. The single-crystal thin-film semiconductor light-emitting element620 includes a GaAs layer (i.e., the light absorbing layer) 625, anAl_(x2)Ga_(1−x2)As layer 624, an Al_(y2)Ga_(1−y2)As layer (an activelayer) 623, an Al_(z2)Ga_(1−z2)As layer 622 and a GaAs layer 621laminated in this order from the bottom (i.e., on the dielectric layer561 side). As described in Example 3-2, the common electrode 554, themetal layer 553 and the electrode 552 are provided on the single-crystalthin-film semiconductor light emitting elements 620 and 630 via theinsulation film 551 as an interlayer insulation film. The metal layer553 also functions as an individual electrode of the single-crystalthin-film semiconductor light-emitting element 630 (on the right in FIG.18). The electrode 552 functions an individual electrode of thesingle-crystal thin-film semiconductor light-emitting element 620 (onthe left in FIG. 18).

According to Example 3-2, the lights emitted by the light-emittinglayers (i.e., the active layers) 623 and 633 of the adjacent twosingle-crystal thin-film semiconductor light-emitting elements 620 and630 toward the GaAs layers (i.e., the light absorbing layers) 625 and631 are absorbed by the GaAs layers 625 and 631, and the lights emittedby the light-emitting layers 623 and 633 away from the GaAs layers 625and 631 are emitted outside as emitted lights 116 and 136.

In the third embodiment (and examples and modification thereof), thedisplay devices using AlGaAs-based single-crystal thin-filmsemiconductor light-emitting elements have been described. However, thesingle-crystal thin-film semiconductor light-emitting elements are notlimited to the AlGaAs-based single-crystal thin-film semiconductorlight-emitting elements, but AlGaInP-based or GaN-based single-crystalthin-film semiconductor light-emitting elements can also be used.

In the above described embodiments, examples and modifications, thelight-emitting elements have been described as light-emitting diodes(LEDs). However, the present invention is not limited to LEDs, but alsoapplicable to, for example, laser diodes (LDs). In particular, it isadvantageous to apply the present invention to surface-emission typelaser diodes or the like. In such a case, for example, uncooled laserdiodes are expected to be accomplished.

Further, in the above described embodiments, examples and modifications,the light-emitting elements used in the display device have beendescribed. However, the present invention is also applicable to, forexample, a thin double-sided display/sensor device having both functionsof double-sided display and double-sided sensor and using single-crystalthin-film semiconductor light-emitting element and single-crystalthin-film semiconductor light receiving element.

Furthermore, the present invention is applicable to applications inwhich the single-crystal thin-film semiconductor light-emitting elementis used in a state where the base substrate (i.e., which is not aneffective operation region of a device) is separated therefrom. Forexample, the present invention is applicable to high-powerhigh-frequency semiconductor electronic devices such asnitride-semiconductor high electron mobility transistors (HEMT).

According to an aspect of the present invention, there is provided adisplay device including a transparent substrate, and a plurality ofsingle-crystal thin-film semiconductor light-emitting elements disposedon one side of the transparent substrate. Each of the single-crystalthin-film semiconductor light-emitting elements is composed ofsingle-crystal thin-film semiconductor layers separated from a basesubstrate, and includes a light-emitting layer (for example, an activelayer) and two non-light-emitting layers disposed on both sides of thelight-emitting layer. The non-light-emitting layer preferably has ahigher energy band gap than the light-emitting layer.

With such a configuration, the base substrate (for forming thesingle-crystal thin-film layers) does not exist in the display device,and therefore lights emitted the light-emitting layer are emittedoutside.

Further, it is preferable to display images on both sides of thetransparent substrate using light emitted from first sides of thesingle-crystal thin-film semiconductor light-emitting elements, andusing light emitted from second sides of the single-crystal thin-filmsemiconductor light-emitting elements and passing through thetransparent substrate.

Furthermore, it is preferable to arrange a plurality of single-crystalthin-film semiconductor light-emitting elements one-dimensionally ortwo-dimensionally.

With such a configuration, images can be displayed on both sides of thetransparent substrate using the lights emitted from the light-emittinglayer.

Moreover, it is preferable that a drive control circuit reverses ascanning direction (along which light emission signals are sent to thesingle-crystal thin-film semiconductor light-emitting elements) atconstant time intervals.

With such a configuration, the same images can be alternately displayedon both side of the transparent substrate for constant time periods.

Further, it is preferable to dispose a first single-crystal thin-filmsemiconductor light-emitting element on the transparent substrate, and asecond single-crystal thin-film semiconductor light-emitting element onthe first single-crystal thin-film semiconductor light-emitting elementvia a non-light-transmission layer. The first and second single-crystalthin-film semiconductor light-emitting elements are respectivelycomposed of different single-crystal thin-film semiconductor layers withdifferent light-emitting layers.

In particular, the non-light-transmission layer can be configured toreflect or absorb lights emitted by the light-emitting layers of thefirst and second single-crystal thin-film semiconductor light-emittingelements.

It is advantageous to provide a drive control circuit that independentlycontrols light emissions of the first and second single-crystalthin-film semiconductor light-emitting elements on both sides of thenon-light-transmission layer.

With such a configuration, images can be independently displayed on bothside of the transparent substrate.

Moreover, it is preferable to provide first and second single-crystalthin-film semiconductor light-emitting elements on the transparentsubstrate so as to be adjacent to each other. A firstnon-light-transmission layer may be formed on a top of the firstsingle-crystal thin-film semiconductor light-emitting element, and asecond non-light-transmission layer may be formed between the secondsingle-crystal thin-film semiconductor light-emitting element and thetransparent substrate.

The first and second non-light-transmission layers preferably reflect orabsorb lights emitted by the first and second single-crystal thin-filmsemiconductor light-emitting elements.

Additionally, a combination of the first and second single-crystalthin-film semiconductor light-emitting elements may be arrangedone-dimensionally or two-dimensionally.

Further, it is advantageous to provide a drive control circuit thatindependently controls light emissions of the first and secondsingle-crystal thin-film semiconductor light-emitting elements adjacentto each other on the transparent substrate.

With such a configuration, images can be independently displayed on bothsides of the transparent substrate. Moreover, pixels as seen from bothsides of the transparent substrate can have different sizes andarrangement pitches. For example, pixels as seen from both sides of thetransparent substrate can have different sizes when the semiconductorlight-emitting elements laminated via the non-light-transmission layer(as in FIGS. 10 and 13) have different surface areas, or when thesemiconductor light-emitting elements disposed adjacent to each other soas to emit lights in directions opposite to each other (as in FIGS.16-18) have different surface areas. Further, pixels as seen from bothsides of the transparent substrate can have different arrangementpitches when the semiconductor light-emitting element(s) emitting lightin one direction and the semiconductor light-emitting element(s)emitting light in opposite direction are different in number per unitarea.

While the preferred embodiments of the present invention have beenillustrated in detail, it should be apparent that modifications andimprovements may be made to the invention without departing from thespirit and scope of the invention as described in the following claims.

1. A display device comprising: a transparent substrate, and a pluralityof single-crystal thin-film semiconductor light-emitting elementsdisposed on one side of said transparent substrate, wherein each of saidsingle-crystal thin-film semiconductor light-emitting elements iscomposed of single-crystal thin-film semiconductor layers separated froma base substrate, and includes a light-emitting layer and twonon-light-emitting layers disposed on both sides of said light-emittinglayer.
 2. The display device according to claim 1, wherein each of saidnon-light-emitting layers has a higher energy band gap than saidlight-emitting layer.
 3. The display device according to claim 1,wherein images are formed on both sides of said transparent substrateusing lights emitted from first sides of said single-crystal thin-filmsemiconductor light emitting elements, and lights emitted from secondsides of said single-crystal thin-film semiconductor light emittingelements and passing through said transparent substrate.
 4. The displaydevice according to claim 1, wherein said single-crystal thin-filmsemiconductor light-emitting elements are arranged one-dimensionally ortwo-dimensionally.
 5. The display device according to claim 1, furthercomprising a drive control circuit that sends light emission signals tosaid single-crystal thin-film semiconductor light-emitting elementsalong a scanning direction, wherein said drive control circuit reversessaid scanning direction at constant time intervals.
 6. The displaydevice according to claim 1, wherein said single-crystal thin-filmsemiconductor light-emitting elements include: a first single-crystalthin-film semiconductor light-emitting element disposed on saidtransparent substrate, and a second single-crystal thin-filmsemiconductor light-emitting element formed on said first single-crystalthin-film semiconductor light-emitting element via anon-light-transmission layer, wherein said first and secondsingle-crystal thin-film semiconductor light-emitting elements arerespectively composed of different single-crystal thin-filmsemiconductor layers with different light-emitting layers.
 7. Thedisplay device according to claim 6, wherein said non-light-transmissionlayer reflects or absorbs lights emitted by said light-emitting layersof said first and second single-crystal thin-film semiconductorlight-emitting elements.
 8. The display device according to claim 6,further comprising a drive control circuit that independently controlslight emissions of said first and second single-crystal thin-filmsemiconductor light-emitting elements disposed on both sides of saidnon-light-transmission layer.
 9. The display device according to claim1, wherein said single-crystal thin-film semiconductor light-emittingelements include first and second single-crystal thin-film semiconductorlight-emitting elements which are disposed adjacent to each other,wherein a first non-light-transmission layer is formed on a top of saidfirst single-crystal thin-film semiconductor light-emitting element, andwherein a second non-light-transmission layer is formed between saidsecond single-crystal thin-film semiconductor light-emitting element andsaid transparent substrate.
 10. The display device according to claim 9,wherein said first non-light-transmission layer and said secondnon-light-transmission layer reflect or absorb lights respectivelyemitted by said first and second single-crystal thin-film semiconductorlight-emitting elements.
 11. The display device according to claim 9,wherein a combination of said first and second single-crystal thin-filmsemiconductor light-emitting elements are arranged one-dimensionally ortwo-dimensionally.
 12. The display device according to claim 9, furthercomprising a drive control circuit that independently controls lightemissions of said first and second single-crystal thin-filmsemiconductor light-emitting elements.